Existing phased array antennas include a wide variety of configurations for various applications, including communication systems. Example communication systems include personal communication service (PCS) systems, satellite communication systems and aerospace communication systems, which require such characteristics as low cost, light weight, low profile, and a low sidelobe.
These desirable characteristics are provided in general by printed circuit antennas. The simplest forms of printed circuit antennas are microstrip antennas wherein flat conductive elements, such as dipole antenna elements, are spaced from a single essentially continuous ground plane by a dielectric sheet of uniform thickness.
In general, the radiation pattern of a phased array antenna is determined by specifying the antenna element currents in both magnitude and phase. The spacing between antenna elements in such an array is usually less than one-half wavelength, and inter-element coupling can limit performance. In particular, the antenna element currents together with this inter-element coupling produces an input impedance to each antenna element that may be different from the usual impedance of the individual antenna elements.
An example phased array antenna comprising an array of dipole antenna elements is disclosed in U.S. Pat. No. 6,512,487 to Taylor et al., which is incorporated herein by reference in its entirety and which is assigned to the current assignee of the present invention. The phased array antenna exhibits a wide bandwidth (about 9:1), but is matched only moderately well over much of the band. The impedance match with the individual dipole antenna elements tends to degrade as the bandwidth is increased. Since antenna gain is related to the quality of this impedance match, antenna performance is typically reduced as the impedance match degrades.